In general, a metal can used as a storage container of beverage is mainly made of aluminum or iron.
The metal can is formed by performing a drawing process, an ironing process, etc. on an aluminum plate or an iron plate in multiple stages.
Moreover, the metal can is divided into an easy open end can and a can provided with a bottleneck, and the metal can provided with a bottleneck is called a necking can, bottle can, neck-in can, etc. (hereinafter, referred to as “necking can”).
The necking can is subjected to a neck-in process to reduce the entrance and form a screw thread such that a cap is connected to the entrance (see FIG. 1).
Next, a conventional apparatus for manufacturing necking cans will be described with reference to FIG. 2.
As shown in FIG. 2, a conventional apparatus 10 for manufacturing necking cans comprises an upper press plate 11 which moves linearly up and down and a lower press plate 12 which rotates to transfer the can to the next process.
Moreover, a plurality of molds 13 are provided on the upper press plate 11 to gradually reduce the entrance of each can for which the drawing process is completed, and a plurality of holders 14 into which the cans are inserted are provided on the lower press plate 12.
Furthermore, a circular guide 15 is provided on the lower press plate 12 such that the holders are mounted thereon.
Meanwhile, the lower press plate 12 is rotated by the driving force of a motor 16.
Accordingly, in the conventional apparatus 10 for manufacturing necking cans, the mold 13 gradually reduces the entrance of the can by the up-and-down linear motion of the upper press plate 11, and the lower press plate 12 rotates to transfer the can fixed in the holder 14 to the next process (i.e., to the next mold).
As such, the entrance processing and the transfer operation are continuously performed such that the cylindrical can is formed into a bottle shape while its entrance is gradually reduced, and the can formed into a bottle shape has a screw thread formed on the top of the can, on which a cap is sealed, by a sealing lip mold as shown in (c) of FIG. 1 and has a curled end as shown in (d) of FIG. 1, thereby completing a necking can.
However, according to the conventional apparatus 10 for manufacturing necking cans, the cans are transferred in a rotating manner, and thus the holders 14 are shaken by inertia, which is very problematic.
In order to prevent the holders 14 from being shaken, the rotational transfer speed of the lower press plate 12 may be limited or a soft strengthening material (such as leather or synthetic resin) may be disposed between the holder 14 and the guide 15. However, this results in loss of productivity and replacement of the strengthening material due to wear, which requires a lot of supplies.
Moreover, according to the conventional apparatus 10 for manufacturing necking cans, the plurality of molds 13 and holders 14 should be replaced and set one by one, and thus it is very inconvenient to process necking cans of various sizes.
In addition, as the replacement time of the molds 13 and the holder 14 increases, the productivity is reduced.